A common and well known type of carrier conveyor system comprises a plurality of work carriers, such as wheeled carriers or skids, which are moved along a predetermined path by a main conveyor underlying and engaging the carriers. As the carriers are moved along, workers commonly perform various tasks on the work carried by the carriers. Thus, for example, workers may apply or work upon portions of an automobile body supported by the carriers. In order to obtain optimum efficiency, the carriers are placed in close longitudinally spaced relation to one another. In such systems, the carrier can be disengaged from the main conveyor as required.
With the advent of automated machines such as robots, it is desirable to be able to perform some tasks on the work with such machines. However, such machines may require interruption of the flow of the work carrier for a predetermined period of time and thus the work carrier must be disengaged from the main conveyor. After the task is performed by the machine, the carrier is re-engaged with the main conveyor. Once again to insure optimum efficiency, the carrier must be disengaged with the main conveyor and re-engaged with the main conveyor quickly without the loss of the original job spacing and sequence on the main conveyor.
Automated work stations can be inserted into manned assembly conveyors either by making the automation mobile to perform tasks "on the fly", or by providing closer job spacing with sufficient accumulation before and after a fixed automated work station. The second method is often preferable because of much lower cost and higher reliability of robotic equipment operating on stationary work.
However, an excessively long distance would be required to provide work time on a slow moving close job spaced conveyor, as is common in the automotive industry. It is therefore, desirable to provide some intervening means of speeding the flow of product (jobs) without disrupting the normal operation of the conveyor. Such a conveyor device would reduce the space and time required to a practical minimum.
Many methods of high speed castered truck transfer have been devised; however, they all have one or more of the following deficiencies:
The trucks are moved on their own casters at high speed, causing fast deterioration. PA1 High noise level. PA1 A high truck modification cost. PA1 Reciprocating devices which cause lost time and additional motion and wear. PA1 An assortment of auxiliary equipment and numerous controls are required. PA1 Floor pits or a significant conveyor elevation changes are required. The latter usually results in long ramps resulting in wasted plant space. PA1 Higher speeds are hindered by the physical limitations of the mechanisms employed. PA1 Relatively high maintenance requirements.
As an example, mechanisms have been heretofore proposed for such transfer of the carriers to and from the work station including mechanical and hydraulic devices for grasping the carrier, transferring it to the work station and returning it to the main conveyor. Such devices have been complex and costly to build and maintain.
Accordingly, among the objectives of the present invention are to provide a conveyor system which will remove a work carrier from engagement with the main conveyor, transfer it to the work station, and return it from the work station to the conveyor in the shortest possible distance while making it possible to maintain a proper supply of carriers in advance of and beyond the work station to insure that the remainder of the system has a carrier at each job space of the main conveyor; which has a low profile; which is accessible for service; which provides ready access to the work station; which is in the normal path of the conveyor; which is low in cost; which is modular and can be adapted to various systems; which provides a degree of redundancy to permit operation even if a portion of the system malfunctions; which functions without substantial lifting of the carrier; which requires minimal change in the construction of the main conveyor; which requires minimal change, if any to the work carrier; and/or which can be retrofitted to conventional carrier systems.
One commercially successful prior conveyor system which also achieves the foregoing objects is that set forth in U.S. Pat. No. 4,564,100 issued Jan. 14, 1986 in the name of Edward E. Moon and assigned to the assignee of record herein. The present invention provides an improvement in the system, method and apparatus of the Moon '100 patent while achieving the aforementioned objects and retaining the advantages of the '100 patent system, as well as achieving further objects and providing additional advantages thereover as set forth hereinafter.